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The family of an Auckland man have taken their pursuit for answers into the death to the coroner, as an inquest into how he died begins in Hamilton today.

Lewis Kenneth John Baker, 75, was in Tauranga with his wife Elizabeth when he began experiencing chest pains in February 2014.

He was admitted to Tauranga Hospital before being transferred to Waikato Hospital for a bypass procedure on March 6, 2014.

While the surgery was carried out successfully, the Baker family say it was his post-operative care in the hospital's intensive care unit - where he eventually died after suffering a cardiac arrest - that led to his death.

The cause of his death is the centre of a coroner's inquest being led by Chief Coroner Judge Deborah Marshall in Hamilton.

The hearing is set down for five days with three Waikato Hospital staff given interim name suppression.

Elizabeth Baker was the first to give evidence this morning and told the inquest how her healthy husband went in for the bypass operation before coming out in a coffin.

The surgery was carried out between 1pm and 6pm on March 6.

He suffered a cardiac arrest about 6.40am the next day.

He was declared dead at 11.15am on March 7.

Baker said she had no problems with the surgery itself, but told Judge Marshall the lack of post-operative care around her husband was "incomprehensible".

She said they'd been married for 50 years and had six children together, one of whom, died as an infant.

Prior to his surgery her husband was healthy and active and was a former head of Physical Education at Auckland's Avondale College.

In more recent times, the couple had been enjoying travelling together and three years ago moved over from Australia and buying a house in Tauranga.

She had no reason to believe he was unhealthy.

Baker, a former nurse, said it wasn't until she got the notes from the surgery in relation to his death that she began asking questions which ultimately led to an inquest being held.

One of the nurses, who has name suppression and cared for Baker in his last hours, said she did notice his condition was starting to deteriorate but her suggestions of how to deal with it were over-ruled by the senior doctor on duty.

While on her 40 minute break from 3.30am, Baker was stable and being monitored.

However, by 4.40am she started to notice his fluid levels changing.

She said she suspected he was beginning to suffer renal failure from about 5am. She reported her concerns to the doctor who disagreed and ordered more red blood cells be given.

By this stage, Baker was becoming "confused and disorientated" and said he was in a lot of pain as he needed to go to the toilet.

However, a check of his bladder discovered it was empty.

She said the nurse she was working with agreed with her observations.

The nurse asked the doctor to get a second opinion but she said she was told that the doctor was asleep.

By 6am, his urine level had dropped to 10mls - from a normal 35ml - and his blood pressure was 60 beats per minute (bpm).

At 6.30am, Baker was "white" and became confused and drowsy, trying to get out of bed.

She immediately began CPR. Shortly afterwards she called Baker's family and told them "he was in a bad way" and to get to hospital immediately.

He was pronounced dead at 11.15am.

Giving evidence earlier in the day and during questioning from Tui, Dr Lin said he was called about the emergency at 6.40am and was in the theatre about five minutes later.

He said it was too late to save Baker by the time he had gone into cardiac arrest.It may have been "possible" to save him if he had been notified earlier, he said.